The present invention relates to a fluid discharge apparatus, and a fluid discharge method, which are capable of feeding fluid at a minute flow rate with high accuracy in fields such as consumer products, information-processing equipment, equipment for factory automation, and production machines.
With employment of the present invention, a fluid discharge apparatus and a fluid discharge method can be provided which are capable of discharging intermittently or continuously various types of fluid in a constant amount, such as adhesives, solder paste, fluorescent substances, grease, paints, hotmelt, chemicals, and foods. The method and apparatus can also be used in production processes for such fields as electronic components and household electric appliances.
Liquid discharging apparatus (dispensers) have been conventionally used in various fields, and techniques for controlling discharge of a minute amount of fluid material with high accuracy and stability have been demanded with needs for miniaturization and increased recording density of electronic components in recent years.
There is also a great demand for a fluid discharging method for applying fluorescent substances uniformly to display surfaces of a CRT (Cathode Ray Tube) and a PDP (Plasma Display Panel), for example.
In the field of surface mounting technology (SMT), for example, requests of dispensers with regard to trends of speed-up, miniaturization, densification, quality improvement, and automation of mounting are summarized as follows.
(i) increase in accuracy in an amount of application
(ii) reduction in discharging time
(iii) minimization in an amount of application in one operation
(iv) diameter reduction in and miniaturization of a dispenser body
(v) equipment with multi-nozzles.
As liquid discharging apparatus, conventionally, such dispensers employing an air pulse system as shown in FIG. 21 have been widely used, and this technique is presented, for example, in xe2x80x9cJidoka-gijutsu (Mechanical automation)xe2x80x9d, vol. 25, No. 7, ""93. A dispenser of this system applies a constant amount of air supplied from a source of a constant pressure into a vessel (cylinder) 150 in pulsed manner, and discharges from a nozzle 151 a certain amount of liquid corresponding to a pressure increase in the cylinder 150.
On the other hand, micropumps employing piezoelectric elements have been developed for a purpose of discharging fluid at a minute flow fate. For example, the following is presented in xe2x80x9cCho-onpa TECHNO (ultrasonic TECHNO)xe2x80x9d, the June issue, ""59. FIG. 22 is a figure of a principle of such a micropump, and FIG. 23 illustrates its concrete structure., Upon application of a voltage to a laminated piezoelectric actuator 200, the actuator undergoes a mechanical elongation, which is magnified by action of a displacement magnifying mechanism 201. Then, a diaphragm 203 is pushed upwardly in FIG. 22 via a thrust-up rod 202, and capacity of a pump chamber 204 therefore decreases. At this time, a check valve 206 in a suction opening 205 closes, and a check valve 208 in a discharge opening 207 opens and fluid in the pump chamber 204 is discharged. Upon a reduction in the applied voltage, subsequently, the mechanical elongation decreases with the reduction in the voltage. The diaphragm 203 is then pulled back downwardly by a coiled spring 209 (by returning action) and capacity of the pump chamber 204 increases and pressure in the pump chamber 204 turns negative. The negative pressure opens the check valve 206 in the suction opening and the pump chamber 204 is filled with fluid. At this time, the check valve 208 in the discharge opening remains closed. The coiled spring 209 has an important role of applying a mechanical pre-load to the laminated piezoelectric actuator 200 via the displacement magnifying mechanism 201, in addition to the action of pulling back the diaphragm 203. After that, the above operations are repeated.
It is thought that a miniature pump having a minute flow rate with excellent accuracy with respect to flow rate can be obtained with the above configuration using a piezoelectric actuator.
Among the above-mentioned prior art, dispensers of air pulse systems had the following issues.
(1) variation in discharge amount resulting from pulsation of discharge pressure
(2) variation in discharge amount resulting from a water head difference
(3) change in discharge amount resulting from a change in viscosity of liquid.
The shorter cycle time (tact) and discharge time are, the more remarkable the phenomenon of the above-mentioned first issue. Therefore, there have been made such contrivances as provision of a stabilizer circuit for equalizing heights of air pulses.
The above-mentioned second issue occurs for the following reason. Capacity of a cavity 152 in the cylinder varies with a residual quantity H of the liquid, and therefore, a degree of a change in pressure in the cavity 152 caused by discharge of a given amount of high-pressure air varies enormously with the quantity H. As a consequential issue, a decrease in a residual quantity of the liquid reduces an amount of application, e.g., by fifty to sixty percent as compared with a maximum amount. Therefore, remedies that have been adopted include detection of the residual quantity H of the liquid during each discharge operation, and subsequent adjustment of a pulse duration in order to make a discharge amount uniform.
The above-mentioned third issue occurs in a case that viscosity of a material, for example, containing a large quantity of solvent changes with time. As an example of remedies which have been adopted for this issue, a tendency of viscosity change with respect to a time axis is previously programmed into a computer and, for example, pulse length is adjusted so that influence of viscosity change may be corrected.
Any of the remedies for the above-mentioned issues has not served as a fundamental solution, because these remedies complicate a control system including a computer, and have difficulty in accommodating irregular changes in environmental conditions (e.g., temperature).
The following is a predicted issue in adaptation of an above-mentioned piezo-pump, using the laminated piezoelectric actuator shown in FIGS. 22 and 23, to high-speed intermittent application of high viscosity fluid employed in such fields as surface mounting.
In the field of surface mounting, a dispenser which is capable of applying, e.g., not more than 0.1 mg of adhesive (having a viscosity in the range of one hundred thousand to one million CPS) instantaneously within 0.1 sec. has been demanded in recent years. It is therefore presumed that such a dispenser requires a high hydrostatic pressure in the pump chamber 204, and high responsibility of the suction valve 206 and the discharge valve 208 communicating with the pump chamber 204. For a pump equipped with a passive discharge valve and a passive suction valve, however, it is extremely difficult to intermittently discharge rheological fluid, having extremely poor fluidity and high viscosity, with high accuracy in flow rate and at a high speed.
In order to eliminate the above-mentioned defects of an air pulse system, a piezo system employing a laminated piezoelectric actuator and the like, and a pump for a minute flow rate that will be described below, has been already proposed by the inventor(in Japanese Unexamined Patent Publication No. 10-128217).
Suction action or discharge action of this pump is obtained by applying relative linear motion and relative rotational motion between a piston and a cylinder by virtue of independent actuators, and electrically and synchronously controlling operation of the actuators.
In FIG. 24, reference numeral 301 denotes a first actuator composed of a laminated piezoelectric element. Numeral 302 denotes a piston driven by the first actuator 301, and the piston corresponds to a direct-acting part of a pump. Between the piston 302 and a lower housing 303 is formed a pump chamber 304, of which capacity changes with movement of the piston 302 in its axial direction. In the lower housing 303 are formed a suction bore 305 and discharge bores 306a and 306b, all of which communicate with the pump chamber 304.
Numeral 307 denotes a second actuator that causes a relative rotational or rocking motion between the piston 302 and the lower housing 303, and the second actuator is composed of a pulse motor, a DC servo motor, or the like. Numeral 308 denotes a motor rotor constituting the second actuator 307 and numeral 309 denotes a stator.
A rotating member 310 is connected to the piston 302 via a leaf spring 311 shaped like a disk. The leaf spring 311 has a shape that easily undergoes elastic deformation in an axial direction in order to transmit expansion and contraction of the piezoelectric element, as the first actuator 301, in the axial direction to the piston 302. Rotation of the rotating member 310 is transmitted to the piston 302 via the leaf spring 311. This arrangement permits the piston 302 of the pump to make a rotational motion and a linear motion simultaneously and independently.
Reference numeral 312 denotes a coupling joint for supplying power from an exterior to the first actuator 301 that makes a rotational motion.
A discharge sleeve 314 having a discharge nozzle 313 at a tip is installed on a lower end portion of the lower housing 303. On an internal surface of the discharge sleeve 314 is formed a flow passage 315 that provides communication between the discharge bores 306a, 306b and the discharge nozzle 313. On surfaces of the lower housing 303 and the piston 302 which undergo the relative movement, are formed flow grooves 316b and 317b which allow alternate communication between the pump chamber 304 and the suction bore 305, and between the pump chamber 304 and the discharge bores 306a, 306b, with relative rotational motion of the lower housing and the piston. These flow grooves play roles of a suction valve and a discharge valve of a conventional pump. Reference numeral 318 denotes a displacement sensor and numeral 319 denotes a rotating disk fixed to the piston 302. A position of the piston 302 in the axial direction is detected by the displacement sensor 318 and the rotating disk 319.
It is thought that, among the requests of dispensers mentioned at the beginning herein, (i) increase in accuracy in an amount of application, (ii) reduction in discharging time, and (iii) minimization in an amount of application during one operation can be achieved by the above-mentioned dispenser shown in FIG. 24, because this dispenser is a positive displacement pump composed of a combination of a reciprocating piston and cylinder.
It is, however, difficult for the dispenser to meet the remainder of the requests, i.e., (iv) diameter reduction in and miniaturization of a dispenser body and (v) equipment with multi-nozzles.
In the above-mentioned dispenser shown in FIG. 24, the piezoelectric actuator is used for linear motion and the motor is used for rotational motion.
Besides, power for conversion of electric energy into mechanical energy is required to be applied to an electrode of the rotating piezoelectric element via a conductive brush (a coupling joint).
The above arrangement also requires a bearing and the displacement sensor to be provided in an area surrounding a rotational axis, and thus has a limit with regard to accommodating the requests of diameter reduction of a dispenser body, and equipment with multi-nozzles.
The present invention has been contrived, taking notice of the fact that a positive displacement pump, for example, can be constituted by a combination of two independent linear-motion devices in consideration of phases of motion of these devices. An object of the present invention is to provide a fluid discharge apparatus and method which can apply, for example, a minute amount of powder and granular material, having an extremely high viscosity, at a super high speed and with high accuracy, and can realize substantial diameter reduction in and miniaturization of a dispenser body and simplification of arrangement.
In accomplishing these and other aspects, according to an aspect of the present invention, there is provided a fluid discharge apparatus that comprises: a first actuator for relatively moving a piston and a housing; a cylinder which accommodates at least a part of the piston and has a space extending therethrough in an axial direction thereof; a second actuator for relatively moving the cylinder and the housing; a pump chamber defined by the piston, the cylinder, and the housing; and a fluid suction opening and a fluid discharge opening which provide communication between the pump chamber and an exterior thereof
That is, according to a first aspect of the present invention, there is provided a fluid discharge apparatus comprising:
a first actuator for relatively moving a piston and a housing;
a cylinder which accommodates at least a part of the piston and has a space extending therethrough in an axial direction thereof; and
a second actuator for relatively moving the cylinder and the housing relatively, wherein a pump chamber is defined by the piston, the cylinder, and the housing, and a fluid suction opening and a fluid discharge opening are provided for communication between the pump chamber and an exterior thereof.
According to a second aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein the first actuator is installed on a fixing section and moves in an axial direction, and the second actuator is installed on an opposite surface of the fixing section and moves in the same axial direction as the first actuator moves.
According to a third aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein a side of the piston facing the pump chamber has an open end, and a discharge opening is formed on a surface which undergoes relative movement between an end surface of the piston facing the pump chamber and a surface facing the end surface.
According to a fourth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein the pump chamber has a capacity that changes with relative movement between the piston and the housing.
According to a fifth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein the cylinder and the housing are configured so that a flow passage resistance of fluid traveling between the pump chamber and an exterior thereof changes with relative movement between the cylinder and the housing.
According to a sixth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein an end section of the piston facing the pump chamber, and an internal surface section of the cylinder accommodating the end section of the piston, have reduced diameters and are attachable and detachable.
According to a seventh aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein the first actuator and/or the second actuator are actuators of an electro-magneto-strictive type.
According to an eighth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the seventh aspect, wherein the actuator of electro-magneto-strictive type comprises a piezoelectric element or a giant magnetostrictive element.
According to a ninth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the eighth aspect, wherein an element of an electro-magneto-strictive type, and a control circuit for the element, have both functions of an actuator and of a displacement sensor.
According to a tenth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein relative axial positions of the piston and of the housing are controlled on a basis of output from a displacement sensor for detecting the relative axial positions.
According to an eleventh aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein a displacement sensor comprising a hollow rotor for position detection and a stator for position detection, is used for detecting relative axial positions of the cylinder and of the housing.
According to a twelfth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the eleventh aspect, wherein the displacement sensor is of a differential transformer type.
According to a thirteenth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein an axial length of the first actuator is greater than an axial length of the second actuator.
According to a fourteenth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the thirteenth aspect, wherein the first actuator comprises a plurality of actuators arranged along the axial direction.
According to a fifteenth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, having a hybrid actuator structure in which a giant magnetostrictive element is employed for any one of the first actuator and the second actuator, and a piezoelectric element is employed for the other of the first actuator and the second actuator.
According to a sixteenth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein a linear motor or linear motors are employed for any one or both of the first actuator and the second actuator.
According to a seventeenth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, having a linear motor comprising a rod in which radially magnetized cylindrical or solid permanent magnets are laminated, and an electromagnetic coil which surrounds an outer circumference of the rod.
According to an eighteenth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein the piston has a shape of a thin plate which is rectangular in cross section.
According to a nineteenth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein the first actuator and/or the second actuator are laminated piezoelectric elements each having a rectangular cross section.
According to a twentieth aspect of the present invention, there is provided a fluid discharge system comprising: an enclosure section which accommodates a plurality of fluid discharge apparatus as defined in the first aspect; and a fluid feeder for feeding the enclosure section with fluid.
According to a twenty-first aspect of the present invention, there is provided a fluid discharge system as defined in the twentieth aspect, wherein the enclosure section is configured so that a common fluid feeding passage communicates with a plurality of pump chambers of the plurality of fluid discharge apparatus.
According to a twenty-second aspect of the present invention, there is provided a fluid discharge system as defined in the twentieth aspect, wherein giant magnetostrictive elements, from which permanent magnets are omitted, are employed for the first actuator and/or the second actuator, and a common cooling passage for cooling magnetic field coils is formed in the enclosure section.
According to a twenty-third aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein at least one of the first actuator and the second actuator comprises a thin-film piezo element.
According to a twenty-fourth aspect of the present invention, there is provided a fluid discharge apparatus wherein at least one of a first actuator and a second actuator has a function of traveling, or expanding and contracting, with aid of an exterior, electromagnetic and non-contact power supplying device.
According to a twenty-fifth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, comprising a third actuator for producing relative rotation between the cylinder and the housing, and a pump device for feeding fluid forcefully to a discharge side which is formed on a surface that undergoes relative movement between the cylinder and the housing.
According to a twenty-sixth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the twentififth aspect, wherein the pump device is a thread groove pump.
According to a twenty-seventh aspect of the present invention, there is provided a fluid discharge apparatus as defined in the twentififth aspect, wherein the first actuator is a giant magnetostrictive element.
According to a twenty-eighth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein the cylinder and the piston are driven during generally opposite phases.
According to a twenty-ninth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein both end portions of one actuator, that expands and contracts axially, are supported by springs, and output of one end of this actuator is used as the first actuator and output of the other end of this actuator is used as the second actuator.
According to a thirtieth aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein a high-pressure developing source for fluid is provided on an upstream side of the fluid discharge apparatus, and the cylinder and the piston in the fluid discharge apparatus as a fluid control valve are driven during generally opposite phases so as to release or shut off the fluid.
According to a thirty-first aspect of the present invention, there is provided a fluid discharge method comprising:
producing by a first and a second actuator relative movement between a piston and a housing and between a cylinder and the housing, respectively, to open a pump chamber defined by the piston, the cylinder, and the housing, thereby sucking fluid into the pump chamber;
thereafter blocking the pump chamber and a passage on a suction side by driving the second actuator; and
thereafter compressing the fluid in the pump chamber by driving the first actuator and the fluid, and thereby discharging the fluid.
According to a thirty-second aspect of the present invention, there is provided a fluid discharge method as defined in the thirtifirst aspect, wherein in producing by the first and the second actuators the relative movement, the first actuator moves in an axial direction and the second actuator moves in the same axial direction as the first actuator moves.
According to a thirty-third aspect of the present invention, there is provided a fluid discharge method as defined in the thirty-first aspect, wherein in producing by the first and the second actuators the relative movement, a capacity of the pump chamber is changed with the relative movement between the piston and the housing.
According to a thirty-fourth aspect of the present invention, there is provided a fluid discharge method as defined in the thirty-first aspect, wherein in producing by the first and the second actuators the relative movement, relative rotation between the cylinder and the housing is produced to feed the fluid forcefully to a discharge side formed on a surface that undergoes relative movement between the cylinder and the housing.
According to a thirty-fifth aspect of the present invention, there is provided a fluid discharge method as defined in the thirty-first aspect, wherein the relative movement is produced by the first and the second actuators by axially expanding and contracting both end portions of one actuator supported by springs so as to use as the first actuator output of one end of this actuator, and use as the second actuator output of the other end of this actuator.
According to a thirty-sixth aspect of the present invention, there is provided a fluid discharge method as defined in the thirty-first aspect, wherein the cylinder and the piston as a fluid control valve are driven during generally opposite phases so as to cancel a change in capacity of the pump chamber to release or shut off the fluid.
According to a thirty-seventh aspect of the present invention, there is provided a fluid discharge method as defined in the thirty-first aspect, wherein in producing by the first and the second actuators the relative movement between the piston and the housing and between the cylinder and the housing, respectively, fluid that is red fluorescent material is sucked into the pump chamber;
after blocking the pump chamber and a passage on a suction side by driving the second actuator, in compressing the fluid in the pump chamber by driving the first actuator and the fluid, the fluid is lineally discharged to apply the fluid onto a panel of a CRT;
then, in producing again by the first and the second actuators the relative movement between the piston and the housing and between the cylinder and the housing, respectively, fluid that is green fluorescent material is sucked into the pump chamber;
after blocking the pump chamber and a passage on a suction side by driving the second actuator, in compressing the fluid in the pump chamber by driving the first actuator and the fluid, the fluid is lineally discharged to apply the fluid onto the panel of the CRT;
then, in producing again by the first and the second actuators the relative movement between the piston and the housing and between the cylinder and the housing, respectively, fluid that is blue fluorescent material is sucked into the pump chamber; and
after blocking the pump chamber and a passage on a suction side by driving the second actuator, in compressing the fluid in the pump chamber by driving the first actuator and the fluid, the fluid is lineally discharged to apply the fluid onto the panel of the CRT.
According to a thirty-eighth aspect of the present invention, there is provided a fluid discharge method as defined in the thirty-first aspect, wherein the fluid is fluorescent material or electrode material.
According to a thirty-ninth aspect of the present invention, there is provided a fluid discharge method as defined in the thirty-first aspect, wherein the fluid is fluorescent material in a case where the fluid is discharged onto a CRT.
According to a fortieth aspect of the present invention, there is provided a fluid discharge method as defined in the thirty-first aspect, wherein the fluid is electrode material in a case where the fluid is discharged onto a PDP.
According to a forty-first aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein the fluid is fluorescent material or electrode material.
According to a forty-second aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein the fluid is fluorescent material in a case where the fluid is discharged onto a CRT.
According to a forty-third aspect of the present invention, there is provided a fluid discharge apparatus as defined in the first aspect, wherein the fluid is electrode material in a case where the fluid is discharged onto a PDP.